In general, an original signal transmitted by a certain transmitter (hereinafter, simply called "wanted signal") is always received at a receiving set together with other plural interfering signals. Since the level of distortion in a telecommunication system is determined by the ratio between the power of the wanted signal and total power of all the interfering signals, even if the level of the wanted signal is much higher than each of the interfering signals, the distortion of the communication system can pose a serious problem when the total power of all the interfering signals proportionally increased according to the number of the interfering signal is rather high.
In conventional telecommunication systems, interfering signals make it very difficult to extract the information from the wanted signal.
Although an array antenna system has been considered as a countermeasure to improve the problems caused by the interfering signals, no practical method of synthesizing the array antenna system in an actual telecommunication systems has yet been suggested. The problems of applying conventional array antenna systems, which is based on the method of Eigen-Decomposition, is mainly due to its complexity and operating speed which is too large for the real-time processing in telecommunications systems.
The conventional technique about the array antenna system was introduced in the following references:
[1] M. Kaveh and A. J. Barabell, "The Statistical Performance of the MUSIC and Minimun-Norm Algorithms for Resolving Plane Waves in Noise," IEEE Trans., Acoust., speech and signal process., vol. ASSP-34, pp. 331-341, April 1986. PA1 [2] T. Denidni and G. Y. Delisle, "A Nonlinear Algorithm for Output Power Maximization of an Indoor Adaptive Phased Array," IEEE Electromagnetic Compatibility, vol. 37, no. 2, pp. 201-209, May, 1995.
The problems in the conventional method of designing array antenna systems are, first, it requires some knowledge about the location of the wanted signal apriori, and second, it requires so many computations that the real-time processing cannot be performed. Especially when the arrival angle of the wanted signal or the total number of signal sources is unknown, the required amount of computation becomes even larger, which makes it impossible to apply the conventional method of synthesizing the array antenna system to the practical signal environment, such as mobile communications.